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Refer to figure.
Given the following information, calculate the expected obstacle clearance overhead the power lines for a single engine piston aircraft at its FLLTOM (Field Length Limited Take-Off Mass) on a straight out departure from Runway 09 in VMC.

Aerodrome elevation: MSL
Climb gradient: 8%
True airspeed: 110 kt
Headwind component: 20 kt
1 NM = 6080 ft
Height difference = [(Ground distance x TAS)/GS] x Gradient(%)/100

  • A

    319 ft

  • B

    492 ft

  • C

    542 ft

  • D

    892 ft

EASA LO 032.02.04.01.02: For a single-engine aeroplane, calculate the expected obstacle clearance (in visual meteorological conditions (VMC)) given gross climb performance, obstacle height and distance from reference zero.

Thankfully for this question we are provided with a formula! We simply need to calculate each variable in the formula before plugging in the numbers.

GS = TAS - Headwind = 90 kt 
Ground distance = 1.5 x 6080 = 9120 ft

We can use the gross gradient provided for this question, as it is a single engine aeroplane and there is no gross to net conversion for the climb gradient.

Height Difference = [(9120 x 110)/90] x 8/100 = 892 ft

Remember, at the start of the climb at the DER we are at the screen height of 50 ft above the reference zero! This means our height AGL at the end of the climb is 892 + 50 = 942 ft

According to the question figure, the power lines are at 400 ft AGL. So, our obstacle clearance will be 942 - 400 = 542 ft

Note: Seeing "Height difference" in the formula should act as a reminder that it is not just outputting a height or altitude, and that you need to add 50 ft.

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